1. Field of the Invention
The present invention pertains to a panel type heating apparatus comprising a relatively flat sheet of electrically conductive paper mounted between substantially rigid electrically insulated panel pieces which may be readily assembled and disassembled.
2. Background Art
It is known in the art of heating apparatus to utilize various types of electrically resistive elements which generate heat when current is applied thereto for providing localized heating for various applications. One particularly advantageous type of material suitable for uniform localized heating of small areas or elements comprises an electrically conductive paper characterized by binder material having electrically conductive material mixed therein to provide a sheet having conductor properties and exhibiting a finite electrical resistance. This so called electrically conductive paper is particularily advantageous for use in various types of heating elements such as those disclosed in my earlier U.S. Pat. No. 3,781,526. Although the type of electrically conductive paper used in the apparatus disclosed in my earlier patent as well as the apparatus disclosed and claimed herein is superior in many respects to other electrically conductive sheet materials, it has been found desirable in certain applications to improve the overall arrangement of the paper in combination with other elements of structure making up the complete heating apparatus in order to provide improved heating characteristics.
Another problem associated with earlier panel type heating units pertains to the method of attachment of the primary conductors or bus-bars to the conductive paper. It is desirable that the current flow and hence the heating of the paper be fairly uniform to provide maximum distribution of heat and to enhance the life of the material. Earlier methods of attaching the primary conductor elements to the conductive paper include the use of bonding agents or adhesives which are not entirely satisfactory as a means of attaching a metallic conductor element to the paper itself. Certain problems with resistance of the adhesive and the difficulty of controlling the thickness of the adhesive results in uneven distribution of current flow through the heating element.
The aforementioned problems in the development of suitable panel type heating apparatus utilizing electrically conductive paper or the like have been substantially overcome with the improved apparatus of the present invention.